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Biederman" , Carlos Maiolino , linux-fsdevel , Kernel Mailing List Date: Fri, 11 Jun 2021 22:16:27 +0800 In-Reply-To: References: <162322846765.361452.17051755721944717990.stgit@web.messagingengine.com> <162322859985.361452.14110524195807923374.stgit@web.messagingengine.com> <03f6e366fb4ebb56b15541d53eda461a55d3d38e.camel@themaw.net> <21ec3ad11c4d0d74f9b51df3c3e43ab9f62c32b4.camel@themaw.net> Content-Type: text/plain; charset="UTF-8" User-Agent: Evolution 3.38.4 (3.38.4-1.fc33) MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Fri, 2021-06-11 at 16:05 +0200, Greg Kroah-Hartman wrote: > On Fri, Jun 11, 2021 at 09:31:36PM +0800, Ian Kent wrote: > > On Fri, 2021-06-11 at 15:11 +0200, Greg Kroah-Hartman wrote: > > > On Fri, Jun 11, 2021 at 08:56:18PM +0800, Ian Kent wrote: > > > > On Fri, 2021-06-11 at 14:49 +0200, Miklos Szeredi wrote: > > > > > On Wed, 9 Jun 2021 at 10:50, Ian Kent > > > > > wrote: > > > > > > > > > > > > Add a revision counter to kernfs directory nodes so it can > > > > > > be > > > > > > used > > > > > > to detect if a directory node has changed during negative > > > > > > dentry > > > > > > revalidation. > > > > > > > > > > > > There's an assumption that sizeof(unsigned long) <= > > > > > > sizeof(pointer) > > > > > > on all architectures and as far as I know that assumption > > > > > > holds. > > > > > > > > > > > > So adding a revision counter to the struct kernfs_elem_dir > > > > > > variant > > > > > > of > > > > > > the kernfs_node type union won't increase the size of the > > > > > > kernfs_node > > > > > > struct. This is because struct kernfs_elem_dir is at least > > > > > > sizeof(pointer) smaller than the largest union variant. > > > > > > It's > > > > > > tempting > > > > > > to make the revision counter a u64 but that would increase > > > > > > the > > > > > > size > > > > > > of > > > > > > kernfs_node on archs where sizeof(pointer) is smaller than > > > > > > the > > > > > > revision > > > > > > counter. > > > > > > > > > > > > Signed-off-by: Ian Kent > > > > > > --- > > > > > >  fs/kernfs/dir.c             |    2 ++ > > > > > >  fs/kernfs/kernfs-internal.h |   23 +++++++++++++++++++++++ > > > > > >  include/linux/kernfs.h      |    5 +++++ > > > > > >  3 files changed, 30 insertions(+) > > > > > > > > > > > > diff --git a/fs/kernfs/dir.c b/fs/kernfs/dir.c > > > > > > index 33166ec90a112..b3d1bc0f317d0 100644 > > > > > > --- a/fs/kernfs/dir.c > > > > > > +++ b/fs/kernfs/dir.c > > > > > > @@ -372,6 +372,7 @@ static int kernfs_link_sibling(struct > > > > > > kernfs_node *kn) > > > > > >         /* successfully added, account subdir number */ > > > > > >         if (kernfs_type(kn) == KERNFS_DIR) > > > > > >                 kn->parent->dir.subdirs++; > > > > > > +       kernfs_inc_rev(kn->parent); > > > > > > > > > > > >         return 0; > > > > > >  } > > > > > > @@ -394,6 +395,7 @@ static bool > > > > > > kernfs_unlink_sibling(struct > > > > > > kernfs_node *kn) > > > > > > > > > > > >         if (kernfs_type(kn) == KERNFS_DIR) > > > > > >                 kn->parent->dir.subdirs--; > > > > > > +       kernfs_inc_rev(kn->parent); > > > > > > > > > > > >         rb_erase(&kn->rb, &kn->parent->dir.children); > > > > > >         RB_CLEAR_NODE(&kn->rb); > > > > > > diff --git a/fs/kernfs/kernfs-internal.h > > > > > > b/fs/kernfs/kernfs- > > > > > > internal.h > > > > > > index ccc3b44f6306f..b4e7579e04799 100644 > > > > > > --- a/fs/kernfs/kernfs-internal.h > > > > > > +++ b/fs/kernfs/kernfs-internal.h > > > > > > @@ -81,6 +81,29 @@ static inline struct kernfs_node > > > > > > *kernfs_dentry_node(struct dentry *dentry) > > > > > >         return d_inode(dentry)->i_private; > > > > > >  } > > > > > > > > > > > > +static inline void kernfs_set_rev(struct kernfs_node *kn, > > > > > > +                                 struct dentry *dentry) > > > > > > +{ > > > > > > +       if (kernfs_type(kn) == KERNFS_DIR) > > > > > > +               dentry->d_time = kn->dir.rev; > > > > > > +} > > > > > > + > > > > > > +static inline void kernfs_inc_rev(struct kernfs_node *kn) > > > > > > +{ > > > > > > +       if (kernfs_type(kn) == KERNFS_DIR) > > > > > > +               kn->dir.rev++; > > > > > > +} > > > > > > + > > > > > > +static inline bool kernfs_dir_changed(struct kernfs_node > > > > > > *kn, > > > > > > +                                     struct dentry > > > > > > *dentry) > > > > > > +{ > > > > > > +       if (kernfs_type(kn) == KERNFS_DIR) { > > > > > > > > > > Aren't these always be called on a KERNFS_DIR node? > > > > > > > > Yes they are. > > > > > > > > > > > > > > You could just reduce that to a WARN_ON, or remove the > > > > > conditions > > > > > altogether then. > > > > > > > > I was tempted to not use the check, a WARN_ON sounds better > > > > than > > > > removing the check, I'll do that in a v7. > > > > > > No, WARN_ON is not ok, as systems will crash if panic-on-warn is > > > set. > > > > Thanks Greg, understood. > > > > > > > > If these are impossible to hit, great, let's not check this and > > > we > > > can > > > just drop the code.  If they can be hit, then the above code is > > > correct > > > and it should stay. > > > > It's a programming mistake to call these on a non-directory node. > > > > I can remove the check but do you think there's any value in > > passing > > the node and updating it's parent to avoid possible misuse? > > I do not understand the question here, sorry.  It's a static > function, > you control the callers, who can "misuse" it? Yes, I'll drop the test and name the argument parent to make it clear for readers. Ian